Nano tint (AKA as diamond tint, Chrystalline film, and other various names) is another grade of tint for car windows.
While regular tint does help protect the inside of your car from glaring sun and gives UV protection, nano-tint goes a step further. With nano-tint, the material is made so that it actually keeps the inside of the car cooler. Depending on the grade you have installed, it can reject up to 97% of infrared (the heat of the sun) and up to 60% of the heat coming through the windows. Amazingly enough, this can be achieved without the film being any darker. It's made with a special nano-technology within the layers of the film, thus providing more benefit, more protection and without cell phone interference.
Before I put this on my Rover, the Tech gave me a demo. He had a small heat lamp and two glass tiles about 4"x4" in size. One tile was covered with standard tint, the other with nano tint... both at 35% tint grade. He first slid the standard tint tile in to the slot over the heat lamp, asked me to my hand as close to it as possible. My hand remained a good 3" away as I could feel the heat burn build up on my hand. The tech then swapped the tiles, inserting the one with the nano-tint. He asked me to put my hand as close to the heat lamp again. This time, I was able to put my hand immediately in front of the tile, nearly touching the glass tile itself and felt no heat coming through! I was sold on the spot (if you've ever sat in a car here in Arizona triple-digit weather, baking in the sun waiting for the light to change... this kind of technology is a god-send)! So, I had it installed on my Rover and have been thrilled with it every since. I had the 3M brand installed.
Now just finding some time to get my Crosstrek in, so I have the nano put on it as well! Anyway, here are some links that may help you more regarding nano-tint:
3M Window Film Technology Takes Its Turn on the Track in 2012:
MOTORTREND Article on Crystalline Automotive Window Films:
Hope this helps.